Hi Susan! I've played both for several years (at varying levels of proficiency). Here's the differences I've noticed:

Piano is way more visual. You know exactly where every key is by the layout of the keyboard ("C" is always to the left of the two black keys, D is between them, Db/C# is between C&D...etc). If you're a visual person, it's easier to pick up theory on the keyboard.

However, the way you think about music on the piano is different than the way you feel music on the guitar. Guitar is about relationships and "shapes" for chords - for example, an E-chord "shape", barred, can be any (major) chord as you move it up and down the fretboard. Once you can barre, you can play just about any chord. I've tried to teach a couple of piano players how to play guitar, and they focus on learning the notes on the fretboard (and getting frustrated) rather than learning the shapes (first). So, their progress on guitar is slower than it could be.

Also, you can be a proficient rhythm guitarist and jam with just about anyone with a fairly basic repertoire. With piano, I find it hard to get away with "rhythm piano" - there's an expectation of greater ability to solo and improvise in band settings (at least, that's what I've found).

As mentioned earlier, pick one and stick with it for a few years, until you feel you are "proficient" to the level you want to be. If you're picking up piano, I'd recommend finding someone who can teach "faking" - that is a valid piano style which is a lot easier than conservatory, and you can sound good faster (and play in a bunch more settings) than if you take the traditional approach to piano. However, it also emphasizes chording in the right hand (along with the melody) with the bass hand handling a much simpler approach (usually the bass of the chord, maybe octaved, eventually doing arpeggios, like in boogie-woogie).

The other difference I find is that, with piano, each hand can be doing something different. I still don't have this down pat - having one rhythm in the left and another on the right bends my brain a fair bit. I started with guitar before going on to piano (and then stuck with piano for a long time, only coming back to guitar now) and that let me have an instrument I could play in groups (guitar) fairly quickly (basic rhythm, of course) while I built up my piano chops.